1. Field of the Invention
The invention relates generally to wafer handling and support systems and, more specifically, to wafer handling and support systems which do not use tape.
2. Description of the Background
Many different types of semiconductor processing systems require the use of wafer handling systems or wafer support systems. Wafers are comprised of a number of integrated circuits or xe2x80x9cdicexe2x80x9d. Through a dicing process, the dice are cut from the wafer. Traditionally, the dicing process is performed with wafer spindle and blade assemblies having circular cutting blades. Such devices may be obtained commercially from Disco Hi Tec America, Inc., Santa Clara, Calif. The cutting blades are oftentimes nickel-plated with a diamond grit cutting edge to allow for smooth cuts with a minimum amount of splintering of the wafer itself.
It is well known in the art to place the wafers on a surface, known as a xe2x80x9ccutting chuckxe2x80x9d, where the wafers are diced by a cutting blade. During the dicing process, the cutting blade may cut through the wafer and into the cutting chuck itself. That damages the cutting blade, accelerates blade wear, and necessitates premature blade replacement to insure that wafers are not damaged during dicing.
To avoid cutting into the chuck, tape is used to hold the wafer in place on the cutting chuck during the dicing process. It is well known in the prior art to use a wafer frame and adhesive tape to maintain dice in place during the dicing process. The wafer frame is generally flat and defines an opening which is larger than the wafer. The adhesive tape is attached to the wafer frame and stretched across the opening. A wafer is secured to the adhesive tape within the opening, and the frame is secured, for example by a vacuum, to the cutting chuck for dicing. After the dice have been cut, the frame, along with the adhesive tape and the dice, are removed from the cutting chuck. The dice are separated from the adhesive tape, the adhesive tape is removed from the frame, and the frame is reused. The adhesive tape is known as xe2x80x9csticky backxe2x80x9d and is usually a polymer based film such as polyvinyl chloride (xe2x80x9cPVCxe2x80x9d), with an adhesive coating on one side. The adhesive tape is usually about 3 mils thick. The dice stick to the adhesive, so that when the wafer is cut the dice remain in place on the cutting chuck and are not scattered. Because a cutting blade extends slightly below the wafer, the cutting blade is exposed to the adhesive tape. The adhesive binds to the cutting blade, causing accelerated blade wear and xe2x80x9cgumming upxe2x80x9d of the cutting blade. A gummedxe2x80x94up cutting blade reduces the effectiveness of the cutting blade, increases friction between the cutting blade and the wafer, and increases the tendency of the cutting blade to bind and break. Heat is generated from friction between the cutting blade and both the wafer and the adhesive. The faster the cutting blade is moved through the wafer, the more heat is generated, and that heat is increased when the cutting blade is gummed-up. In addition, the risk of the cutting blade binding increases as the temperature of the cutting blade increases. Furthermore, the silicon substrate may be damaged by the heat. As a result, the heat generated by the dicing process, and all of the undesirable side effects of the heat, limits the rate at which the cutting blade can be moved across a wafer. As the rate of the dicing processes decreases, the amount of time required to dice a wafer increases.
The accelerated wear and damage caused to cutting blades from contact with the chuck and the adhesive requires that they be replaced after dicing only about five or six wafers. Worn cutting blades lack exposure of the diamond particles to cleanly cut a wafer. The continued use of a worn cutting blade may result in damaged or totally destroyed wafers caused by a cutting blade breaking and spraying debris across the wafer. Replacing cutting blades is expensive not only in terms of the costs of the cutting blade, but also in terms of down time of the dicing process and interruption of the fabrication process while an old cutting blade is being removed and a new cutting blade is being installed.
Efforts have been made to design systems which do not require the use of tape. One such system is disclosed in U.S. Pat. No. 5,803,797. That patent discloses a patterned chuck with vacuum holes through the chuck to hold the die in place both during and after dicing. The patterned chuck has a plurality of recesses in its surface to accommodate the cutting blade. However, this requires that a special chuck be used for each type and size of die to be cut, as the plurality of recesses on each patterned chuck correspond to the particular type and size of dice to be cut.
Therefore there exists a need for an improved wafer handling system which reduces the amount of wear and damage to the cutting blade while allowing for efficient cutting and that is both economical and time efficient. More specifically, there is a need for a cutting chuck and adherence system that does not interfere with the cutting blade during dicing, but that secures a wafer onto the chuck without the need for a tape adhesive while proving to be cost effective and adaptable for use with a variety of wafers.
One aspect of the present invention is to provide a chuck plate, which includes a non-porous section surrounding a porous section. The chuck plate is sized to be carried by a wafer chuck. A wafer can be located on the porous section and held in place by the application of a vacuum. The chuck plate is then carried, for example, by a cutting chuck. Should the cutting blade extend through the wafer, the blade will cut the metallic porous section of the chuck plate such that damage to the blade is eliminated.
Another aspect of the present invention is to provide a cutting station, which includes: a chuck for supporting a wafer during singulation, a chuck plate carried by the chuck wherein the chuck plate includes a non-porous section surrounding a porous section, a cutting apparatus for cutting a wafer; and a vacuum in communication with the chuck.
Another aspect of the present invention is to provide a wafer handling and support system, which includes a chuck plate comprised of a non-porous section surrounding a porous section, and a robotic arm for transporting a wafer under vacuum. The robotic arm may include: a supporting arm capable of movement in the x, y and z directions, a forceps mechanism connected to the supporting arm and capable of movement in the z direction, and a vacuum wand connected to the supporting arm and in communication with a vacuum pump.
In accordance with another aspect of the present invention, a method is provided which includes the following steps: supporting a chuck plate with a chuck wherein the chuck plate comprises a non-porous section surrounding a porous section; positioning a wafer on the porous section of the chuck plate; applying a vacuum force to the wafer through the chuck and chuck plate; and singulating the wafer.
The present invention provides several advantages over prior art techniques. Yields are increased in comparison to systems that use adhesive tape. Yields are also increased in comparison to systems that require a specialized patterned chuck corresponding to each particular die to be cut. The method of the present invention may be carried out using much of the existing wafer handling equipment. Also, the life of the cutting blade is increased which, in turn, reduces the amount of down time of the dicing process and thus increases output. Those advantages and benefits, and others, will be apparent to those of ordinary skill in the art from the Description of a Preferred Embodiment, herein below.